The present invention relates generally to nuclear reactors and, more particularly, to the removal of cesium from the liquid metal coolant of a fast breeder nuclear reactor.
A typical fast breeder nuclear reactor employs liquid sodium as a coolant to remove the tremendous heat generated by the nuclear fission of fissile materials. The heat carried by the coolant is ultimately transformed into steam via a secondary system for the generation of electrical energy. The liquid sodium is circulated through a closed heat transport system known as the primary coolant system which includes the reactor vessel, a heat exchanger or a steam generator, a suitable piping system for serially connecting these components together, and a pump for circulating coolant therethrough. The liquid sodium can be substantially contaminated by the volatile, radioactive fission products resulting from breached or vented fuel elements during reactor operation. Cesium is known to be one of the dominant radioactive contaminants found in the primary coolant system and its deposition on the cooler surfaces of sodium coolant systems has often been observed. The presence of cesium in the primary coolant system poses a safety and health hazard, especially during reactor refueling, maintenance and/or primary coolant system repairs wherein contact maintenance is required with resultant personnel exposure to the hostile environment. Also, any leakage of the contaminated coolant from this primary system, although highly improbable, would pose further safety risks. Accordingly, it can be appreciated that cesium removal is of paramount importance in reducing the health hazards associated with fast breeder nuclear reactors.
Various attempts have been made to solve this cesium contamination problem including the use of a cold trap purification system. However, this arrangement has been only marginally effective in removing cesium and the extent or magnitude of cesium removal has varied widely. This variability in cesium deposition behavior is believed due to interactions with other contaminants in the sodium system with both oxides and hydrides being proposed as possible contaminants responsible for increased cesium deposition. However, other approaches involving deliberate additions of oxygen and hydrogen, respectively, suggested that oxide and hydrides do not enhance cesium deposition. One of the more successful solutions in removing cesium from a sodium coolant system involves the use of a special carbon packing trap provided in the circulating system of the liquid sodium flow. Such a trap was employed in the sodium coolant system of the Experimental Breeder Reactor II (EBR-II) facility in Idaho Falls, Id. It was found that under relatively low temperature conditions, graphite or amorphous carbon packing employed in the trap could remove about 90% of the cesium activity from the sodium in the primary coolant system.
The present invention constitutes an improvement over this cesium removal system and is directed to a method and system for regenerating the primary carbon packing trap of the primary system to realize further reductions in the cesuim activity therein than has heretofore been possible.
Accordingly, it is a primary object of the present invention to provide a new and useful method and system for more efficiently removing cesium from a reactor coolant.
It is another object of this invention to provide in the primary coolant system of a nuclear reactor a regeneration flow system selectively connected to the primary system's main trap for reducing the cesium inventory otherwise entrained therein.
It is a further object of the present invention to provide a new and useful regeneration method and system for regenerating the main cesium trap in a sodium coolant system and improving its cesium absorption capabilities.
These and other objects, advantages, and characterizing features of the present invention will become clearly apparent from the ensuing detailed description of an illustrative embodiment thereof, taken together with the accompanying drawings wherein like reference characters denote like parts throughout the various views.